The present invention concerns a wind power installation having a control apparatus for operational management of the wind power installation and a method of controlling a wind power installation having a control apparatus for operational management.
A wind power installation converts a part of the kinetic energy contained in the wind into electrical energy. For that purpose the wind power installation has a rotor which takes kinetic energy from the wind and converts it into rotational energy.
DE 198 44 258 A1 discloses a wind power installation and a method for the operation thereof in which, in dependence on sensors, in the presence of the air density at the wind power installation, the operational management system sets the speed at which the wind power installation shuts down at a higher level, with decreasing air density. If therefore, with a normal level of air density, the shut-down speed assumes its predetermined value, the shut-down speed is increased when the air density is less.
Stored in the control apparatus of a wind power installation is a power characteristic which permits the control means of the wind power installation, on the basis of the ascertained rotor speed which is dependent on the wind speed, to ascertain the associated generator power. That generator power which the wind power installation is intended to furnish affords the exciter power required and in turn therefrom the generator moment. In order to produce that required generator moment the rotor must afford at least that rotary moment, by way of the drive train.
The power P of the wind power installation corresponds to the amount of energy flowing through the rotor circuit of the wind power installation and arises out of the cross-sectional area F which corresponds to the circular surface area of the rotor, in accordance with the following equation:P=½ρv3F[W].
At a given wind speed v and a predetermined circular surface area F of the rotor, the foregoing equation gives the dependency of the amount of energy on air density ρ. If the amount of energy is too low the rotor cannot apply that moment and therefore the rotor speed drops as a consequence of the excessively high generator moment.